DE 100 43 006 C1 teaches a device. Here an assembly of plate springs provides a tensile force for clamping a tool or tool holder in a tool mount through a set of collet chuck segments. The tool is released by an axial displacement of a so-called drawbar on which, for this purpose, a corresponding counter force must be applied. This counter force is applied as a compressive force by means of a piston driven hydraulically or pneumatically onto the end face of the drawbar facing away from the tool mount. The piston is therefore designated as a tool release piston. As an alternative, in DE 10 2004 051 031 B3, the use of an electric drive was also proposed for displacing the tool release piston.
For clamping a tool, the tool release piston is moved from its active position, in which it deflects the drawbar against the force of the plate-spring assembly and therefore sets the tool clamping device in the released position, into its inactive position, in which it is not in contact with the drawbar. Because the drawbar rotates during the operation of the operating spindle whose component is the tool clamping device, while the tool release piston stands still, when the operating spindle starts up, there is no longer contact between the drawbar and the tool release piston. In order to guarantee this, after the issuing of the corresponding command by the control unit of the processing machine, a specified time span must elapse before the operating spindle can be started. This time span can last, for a maximum, during the disengagement movement of the tool release piston from the drawbar. This means a certain delay in the work cycle of the processing machine.
In the case of an incorrect function in the form of a disengagement movement of the tool release piston from the drawbar that is too slow or incomplete due to incorrect pressure ratios in the case of a hydraulic or pneumatic drive of the piston or due to an incorrect cycle control by the control unit of the processing machine, the operating spindle may start even though the tool release piston is still in contact with the drawbar. In the extreme case, this can lead to frictional fusing of the tool release piston with the drawbar at the respective pressure contact faces, i.e., to damage to the tool clamping device.